Resistance Soldering Bus Strips to 18650 Cells

[ridethelightning]

are we in the territory of solid state relay controlled by 555 timer circuit here?

i used on for a modification of dn10 spotwelder, but i think it would also work perfectly to time a mot transformer for this application.

 

[fechter]

I've been trying to find examples of resistance soldering for large pieces. Most of them are designed for tiny little SMD parts.
I found a few examples of large work. They appear to be using graphite electrodes, which generate lots of heat.

[youtube]gW9_NX2krMM[/youtube]

It doesn't seem much different than using a large iron but maybe more convenient.

Here is an article about using a triac on an inductive load, like a transformer:
http://www.homemade-circuits.com/2012/04/how-to-use-triacs-for-inductive-loads.html

This one is probably close to what you'd want for a MOT. A higher rating might be nice, but duty cycle will be short.
http://www.galco.com/buy/KB-Electronics/KBWC-215K

 

[spinningmagnets]

Thanks Fechter, and also ridethelightning.

I looked around, and the best bang-for-buck on SAC305 solder-paste seems to be sparkfun, so I ordered a jar. I also ordered copper sheet in various thicknesses (0.15mm - 0.40mm). I think I may be two weeks away from a conclusion. I have a good feeling about this.

SAC means "Sn / Ag / Cu", and the number means 3% Silver, 0.5% Copper (with the remainder being Sn = 96% Tin). Everything in life is a compromise, and there are "low temp" melting solders that typically have 50%-ish Bismuth (Bi), but...Bi is a much worse conductor than Tin, so...its only good for hermetically sealing and mechanically bonding two wires that are already in good contact (twisted together), for that job, Bi-solder would work great. SAC305 conductivity is 13/100 compared to pure copper, but...the conducting shells of these 18650's are steel which is 10/100 at best. If the solder is thin, its better than the conductivity of the can that it's being connected to...

edit: 50-grams for $17, synthetic flux (will have to get it to see if its acid-flux)

https://www.sparkfun.com/products/12878

 

[fechter]

Now, to get really fancy, there are some inexpensive non-contact infrared thermometer chips.

http://www.mouser.com/ds/2/734/MLX90614-Datasheet-Melexis-953298.pdf

This one can be configured to work as a thermostat without a host MCU. You could dial in the desired peak temperature and it would automatically cut the power when the peak was reached. Same units on a little board can be found on eBay.

OK, maybe overkill. Good visibility and a sharp eye can detect melting quite nicely.

Also, if using paste, make sure it isn't acid flux. Not sure if the residue from the good stuff is anything to worry about.

 

[spinningmagnets]

Yes, from what I'm learning, the current is what does the hard work, but...the carbon rods (from a welding supply) that hobbyists often recommend, will get very hot at the tip (glowing), as I have seen on the videos.

Fechter had an idea a while back about spot-welding copper (which had a problem with electrodes sticking to the weld). Using tungsten rods (which have a very high melting temp). Using tungsten at the very tip eliminates sticking, but the tungsten part gets very hot. By inserting a short tungsten rod into a fatter copper rod, the current would take the path of least resistance, and the only part of the tungsten that would get any current is just the tip.

Also, by making the thick copper rod clamping on the tip, it would be easy to swap out tips, to have either a sharp one or a flat tip, depending on the job at hand.

 

[fechter]

The tungsten electrodes might be good in this application.

 

[bedesign]

[pre]Here is an easy solution for the time being, that i hope will make
driving a 900VA 120V MOT RELIABLY? with a TRIAC ST - BTA26, the
same as 'spinningmagnets' have in the Router Controller

Remark - driving a universal motor like a router with a resistance
of more than 1 ohm should work without this 'fix',
though could have some problem with speed control
according to AN306 from ST.

** this has been slightly revised after reading the
application note from ST led to me by 'fechter'
http://www.datelec.fr/secteur/ST%20AN308.pdf

This whole test, driving a demanding MOT will now only
work well if this TRIAC-circuit operating principle is
of the simplest kind i.e synchronized by the voltage
across the TRIAC.
And with the POWER FIXED SET TO 85 PERCENT.
There is no useful info in the manual other than
"don't operate the product while under influence"


PROCEDURE
---------
1.
Add a 10 meter AWG 14 extension cord between the wall socket
and the TRIAC-Unit.
If the house internal AWG 12 wiring from the fuse central to the
wall socket in use is shorter than 10 m, increase the extension
** cord length accordingly to reach the target min. resistance.

2.
** Always turn on and run with the POWER FIXED SET TO 85 PERCENT.
Well, not much use for the power control then ..
but it's needed for reliability reason, like when being used
as a 'relay' for a foot switch


3.
It is important to make sure the HEAT SINK is good enough,
or replace it to keep the temp < 50C
(the TRIAC was the isolated version), though if it explodes ...


Would be interesting to know if it works ..


The boring details and explanation is below -
-------------------------------------------

900VA MOT
Total surge resistance worst case + fix --
10m 12-gauge 3.31 mm2 House wiring+MOT
0,14+0.28 ohm -- 0,42 ohm

Add min. 10m extension cord AWG 14 -- 0.18 ohm
Total 0.60 ohm

TRIAC ST - BTA26 NAX ALLOWED First peak -- 260 A
First peak -- 200 Amp -- 30 PERCENT MARGIN - OK

AVERAGE peak current 10 periods of surge decay --
60 A - OK

This might lower the 'Q'-value by 40 percent and
speed up magnetisation of the core, not sure if
it will have any significant negative influence.

If, it can be compensated for by NOT starting
at more than 75 percent power.

--

Additional later better 'fix' -
A TRIAC Solid state relay 'fixed position' Zero crossover starter,
or an adjustable type set to Zero=100 percent will rather un-
intuitely cause a current surge enormo in transformers -
if untreated in this case - 428 A that repeats and decays for
10 or more periods.

Because the lagging 'previous' reverse core field is missing if it's
a fresh start from Zero level, it can't help center the field swings
and prevent the start field going through the roof - making the
transformer primary winding mostly resistive for up to 0.2 sec.

A way to prevent this is to 'fake' a higher frequency that initially
increases the impedance to limit the current by simply starting at
a higher voltage point on the AC period curve to make a fast
transient.

This will as said before increase the noise, as adjustables will.

So to get the most power out while still not burning the units,
a 'slow start' function is needed, but not too slow in this
application.


I have been demonstrated this effect with a vacuum cleaner that
always triggered a circuit breaker when it was started on 100
percent, but behaved well when started with a lower setting -

A design that indeed sucks ...[/pre]

 

[parabellum]

If one is to impatient to have the fundamentals
sorted out first the result will be "BAD"

Sorry, I agree, overreacted a bit, now going on topic again.

Maybe, smaller transformer rout is the way to go?

It is not spot welding we are after and we have some seconds to produce the heat.
I have 3 junk UPS's, used for PC backup, they are 12 V battery side to ~120V AC IN/OUT.
Transformers winding is split in 2 or 3 places, it acts as V stabilizer as well. I get 180V out of longest wind (moderately loaded), feeding 120V to short one, so every point could be used to vary output 66-100%.
They are somewhere in 400VA-1100VA range, which translates in to 200-600W continuous (manufacturer markings). Transformer can tolerate much more than that in short bursts for sure.

New 200W (400VA) UPS unit costs ~ 30USD equivalent in nearest computer shop.

I wonder how 12V side will react with OEM winding as is, shorted. Will try to take some time and open up small one on Saturday and measure AC current on shorted LV side, and current on HV as well.

 

[bedesign]

If one is to impatient to have the fundamentals
sorted out first the result will be "BAD"

Sorry, I agree, overreacted a bit, now going on topic again.

Maybe, smaller transformer rout is the way to go?

It is not spot welding we are after and we have some seconds to produce the heat.
I have 3 junk UPS's, used for PC backup, they are 12 V battery side to ~120V AC IN/OUT.
Transformers winding is split in 2 or 3 places, it acts as V stabilizer as well. I get 180V out of longest wind (moderately loaded), feeding 120V to short one, so every point could be used to vary output 66-100%.
They are somewhere in 400VA-1100VA range, which translates in to 200-600W continuous (manufacturer markings). Transformer can tolerate much more than that in short bursts for sure.

New 200W (400VA) UPS unit costs ~ 30USD equivalent in nearest computer shop.

I wonder how 12V side will react with OEM winding as is, shorted. Will try to take some time and open up small one on Saturday and measure AC current on shorted LV side, and current on HV as well.

500VA at 12V makes an internal Transformer impedance of
0.3 ohm, if it truly can deliver 40A when shorted.

Theoretically, for max power transfer, the work piece
resistance should be the same.
That would put 120 W into the work piece at a current
of 20A, and the same heating of the transformer.

But that's not the only thing at play here -
CURRENT DENSITY IN THE LOAD seems be the determining thing.

With work pieces for battery connections the resistance
will practically be zero INITIALLY AT ROOM TEMPERATURE,
and for a 30 mm length of awg 14 the resistance would
be 0.0003 ohm and the power in the piece only 0.5 W at
40A while the transformer will be heated with 500 W.

Though ohms/impedance laws may not be the only rule here -
if the current density of 20 A per mm2 in this case
would be enough to heat and increase the resistance,
the power transfer could accelerate.

Test should be made and more info found on the
minimum or optimal current to aim for.

But generally absolutely best is a high enough current
to start the heating and a very low impedance/voltage
feed to protect the transformer.

 

[parabellum]

But generally absolutely best is a high enough current
to start the heating and a very low impedance/voltage
feed to protect the transformer.

Yup, rewinding LV side seems almost inevitable. Will measure resistance of the winding as is first and see what I get on current (with unknown inductance in play is impossible? to calculate mathematically)
What I am sold on are several access points on HV winding, which potentially enables several power stages without thyristor, triac nor Fets. It even could be used on 220V with thermal management in mind.

 

[spinningmagnets]

This looks like what is being done here. The pic is a DIY unit, but it's design was copied from a larger industrial unit. I don't understand it yet.

[labels on top row from left to right = 1V, 1.5V, 3V...lower row 0V, 2V, 4.5V]

 

[parabellum]

This looks like what is being done here. The pic is a DIY unit, but it's design was copied from a larger industrial unit. I don't understand it yet.

Multiple secondary winding access points is nice to. If I replace secondary (LV) will do that as well.

 

[bedesign]

My post -
about driving a 900VA 120V MOT RELIABLY? with a TRIAC ST - BTA26
if it uses a circuit operating principle of the simplest kind
i.e synchronised by the voltage across the TRIAC.
https://endless-sphere.com/forums/viewtopic.php?f=14&p=1302418#p1301889

- has been slightly revised after reading the
application note from ST, led to me by 'fechter'
http://www.datelec.fr/secteur/ST%20AN308.pdf

This paper is VERY good find, as it solves the remaining issues
with heavy transformer driving that also was reported here by
members as "I had mixed results"

Advantages:
- Accuracy of the triggering pulses
- Correct operation for resistive loads
- No bad operation with inductive loads
- Power variation over the whole range
- Good balance between positive and negative current cycles

The reliability has been proved in industrial use.

The base circuit principle as pictured on PDF page 9
should be extended with 'fast soft start' to secure for the
current surge problem described in one of my previous posts
- and more as members gets carried away.

---------

Regarding the secondary winding + ev. taps -
it's recommended to use all available winding
area for the thickest wire possible and not
using connectors because of voltage drops -

50 milliohm with 40 A makes 80 W
better used on the piece to heat

---------

With the sum of the base considerations now covered
in this thread, it should enable people to start
exploring practical circuits - if it would prove
difficult to find these requirements full filled
in standard units - for a reasonable price.

Be very careful and have fun!

 

[spinningmagnets]

Many thanks to Fechter and bedesign for taking the time to look into this. I wouldn't know what questions to ask, and...even if I DO ask the right questions, I wouldn't recognize the correct answers when they were right in front of me.

The writer of this PDF talked about these circuits as if he understood them in depth, and was also seeking the simplest and most robust solution. We don't need a wide variety of features, we just want something that works off of a common 120V AC / 15A outlet with safety, and provides our target of 40A, with as much adjustable range as is easily possible. My dream would be from 10A up to 80A, if possible, but...30A to 50A would still be wonderful achievement if it can be done for under $100 for the complete rig.

 

[parabellum]

Just got some time and unfortunately, only have 1 UPS in my junk pile, because 2nd works perfectly and 3rd was thrown away at last clean-up.

Anyway, remaining one is higher quality ACP 700VA/450W and have some interesting results:
1)Primary winding sees 35A at 120V with secondary shorted
2)Secondary, shorted, shows 280-290A. Only did connect it 4 times for ~ 2 seconds, the 14AWG bridge wire start to stink burning PVC instantly.

Secondary winding is made of ~3mmD wire.
[youtube]P5TsArGUouQ[/youtube]
[youtube]pWXnU9_q_RA[/youtube]

 

[parabellum]

P.S.This APC unit is different to other no name units I got before.

1) It does not have middle point on secondary winding, just the ends.

2) It has no multiple accesses to primary winding, just 2 separate windings a)2Ohm and b)0.5Ohm

In my understanding, it could use the 0.5Ohm winding to fine tune the output voltage for regulation.
My plan is to try using winding b) in series with a), in same and then reversed direction.

Any suggestions?

 

[bedesign]

Anyway, remaining one is higher quality ACP 700VA/450W and have some interesting results:
1)Primary winding sees 35A at 120V with secondary shorted
2)Secondary, shorted, shows 280-290A. Only did connect it 4 times for ~ 2 seconds, the 14AWG bridge wire start to stink burning PVC instantly.

Secondary winding is made of ~3mmD wire.

-------------
primary winding, just 2 separate windings a)2Ohm and b)0.5Ohm

In my understanding, it could use the 0.5Ohm winding to fine tune the output voltage for regulation.
My plan is to try using winding b) in series with a), in same and then reversed direction.

Any suggestions?

That was a real test, guess the house line fuse is 30A?

The good values shows it's over dimensioned,
not marginal as MOTs. So should be a better
choice than a MOT - also it can run idling.
Some MOTs draws much power on the primary
with no load.

The pure resistance value of the primary
would be good to have to find current
surge margins for TRIACs.

If this is switched by a mechanical switch
it will randomly generate a current surge
on the primary that reaches more than 400A

When the good TRIAC circuit from STs AN308 is
used and no additional 'fast slow start' is
implemented, surge suppression will still be
active if the adjustable power is set to
less than 75 percent.

As the power capacity margin is quite good,
a 25 percent decrease could be OK.


Regarding using one primary in reversed
serial direction with the other -
I have never studied that, ...
Edit: wrong assumption removed

To be sure that this won't increase the power
loss, a headlight bulb could be fed from the
secondary - if it's still 12v out.

Then measure primary current with a. winding
alone, then with the reverse included -



Some estimation by data from your test
--------------------------------------
Temperature Coefficient of Copper = +0.40
Nickel = +0.58

Copper heated to 125c will increase resistance by
100 x 0.40 = 40 percent

0.4 x 0.003 = 0.0012
0.003 + 0.0012 = 0.0042 mOhm

Assuming 600VA/450W continuous:

The power transfer gets more efficient when the
temperature of the metal piece increases

---
Output impedance 11 mOhm
With 3 V, the continuous current may be 150 A and the peak 215 A.

A 10 mm dia. or more wire should be used.
Start power in a 3 mOhm piece = 140 W
When at 125c -- 187 W

Internal heating of transformer at 150A = 250 W

 

[parabellum]

Apparently, reversed winding boosts the Voltage on main winding and sure ads some loses.

being
a=main winding 2Ohm
b=secondary winding 0.5Ohm

At no load secondary winding gives me:

1)120VAC on a - 12.4VAC
2)120VAC in serial a+b in one direction- 11.2VAC
3)120VAC in serial a+b in opposite direction- 14.1VAC

Did it yesterday and notes are at home, may be off by a tenth of a V

That was real test, guess the house line fuse is 30A?

Original 10A resettable fuse pops open instantly, so I bypassed it but still did not want to go to breaker panel. That's why 2 seconds only.

 

[bedesign]

Apparently, reversed winding boosts the Voltage on main winding and sure ads some loses.

being
a=main winding 2Ohm
b=secondary winding 0.5Ohm

At no load secondary winding gives me:

1)120VAC on a - 12.4VAC
2)120VAC in serial a+b in one direction- 11.2VAC
3)120VAC in serial a+b in opposite direction- 14.1VAC

* 3)120VAC in serial a+b in opposite direction- 14.1VAC *

I see, then I was only half right -
so what happens with the reversed connection
is that it creates a 'virtual' lower turn primary
that naturally increases the secondary voltage
and some increase in the primary current.
Though I can't yet see the math behind the
practical result if the wire diameter for
A. and B. is the same turn to resistance
relation .. anyway just interesting for now.

 

[parabellum]

Yea, you can go the other way- it cancels turns on main wind.
You can not do much math on inductive load without inductance value and there is no load now, which makes it even worse.
Logically it must fall down in comparison to other combos, at any load and much quicker at any increase, resulting less power available then even in normal (1 winding) position at any time.
My equipment sucks.

P.S. spiningmagnets created nice tread some time ago https://endless-sphere.com/forums/viewtopic.php?f=2&t=89289#p1302358, we could deposit valuable information and results there, if we have any, to keep it clean, kind of "How To", most complicated and most simple way. What do you think?

 

[12-C]

Yes, from what I'm learning, the current is what does the hard work, but...the carbon rods (from a welding supply) that hobbyists often recommend, will get very hot at the tip (glowing), as I have seen on the videos.

Fechter had an idea a while back about spot-welding copper (which had a problem with electrodes sticking to the weld). Using tungsten rods (which have a very high melting temp) eliminates sticking, but the tungsten gets very hot. By inserting a short tungsten rod into a fatter copper rod, the current would take the path of least resistance, and the only part of the tungsten that would get any current is just the tip.

Also, by making the thick copper rod clamping on the tip, it would be easy to swap out tips, to have either a sharp one or a flat tip, depending on the job at hand.

I have been following your and various members stream of thought and various members attempts to weld copper, it's challenges and various successes.

To me it seems the benefit of welding is the near instantaneous transfer in energy with minimal heat transfer but the challenge is making it work at a affordable cost to the hobbyist, while soldering in general it's easy and cheap but risks our batteries to heat exposure.

I have no experience with either welding nor resistance soldering but I wonder if using the various hobby grade welding rigs( couple hundred bucks on eBay) (although they can't weld copper) could they not be able to supply the needed energy to melt a thin layer of solder paste while at the same time minimize heat soaking to the battery cans? Perhaps they may perform this off label function even better than a true resistance soldering unit given the need for minimal heat transfer to our batteries? Perhaps the use of wider or broad electrodes with some lower energy combination/increased duty cycle could actually achieve high enough temps to solder copper to the cans but not actually weld them together? Then the more expensive resistance soldering rigs may not be necessary...

 

[spinningmagnets]

edit: it appears as though these have an output of around 900V DC, so I cannot recommend them for RS

I have purchased a $150 "loaf of bread" mini DC welder to test. It has settings from 10A-to-80A, so it appears it may be useful for that. I am also exploring several other cheaper options that I will post about in a couple weeks when I finally have some results.

 

[sn0wchyld]

just finished and tested a rudimentary MOT setup... secondary puts out 1.3v with 2 turns, and 600A through 2m of 4G wire. Needless to say, 4G is woefully inadequate. 20 seconds and its worryingly hot (the cheapo pvc insulation has softened considerably, not too hot to touch, but hot enough that i need to stop for a while). That said im rather happy with how well it works, despite just using the bare wire in a clamp to hold the piece to be soldered, soldering a 3 way 12g wire splice was almost complete in that 20 second burst (about 2-3 seperate bursts using a foot pedal), something that would have taken 5+min using my 60W iron. Going to get myself some 0 or 00G wire and see how it improves things.
600A certainly makes the wires jump around too! they hang down from a shelf above my workspace, and the magnetic forces are sufficient to push the wires a good 5cm apart!

 

[spinningmagnets]

If you have an extra MOT laying around, there is a promising method of converting it to a variable inductor to limit (adjust) the amps on the MOT that provides the power...

https://endless-sphere.com/forums/viewtopic.php?f=2&t=89289#p1301672

 

[bedesign]

P.S. spiningmagnets created nice tread some time ago https://endless-sphere.com/forums/viewtopic.php?f=2&t=89289#p1302358, we could deposit valuable information and results there, if we have any, to keep it clean, kind of "How To", most complicated and most simple way. What do you think?

I wouldn't know what questions to ask, ...

[pre]Here is a collection of findings and considerations to help making
better choices before beginning a detailed construction.

A PREFERED WAY TO MANAGE THE CURRENT FEED
WITHOUT WEARING STRESSES AND VASTED POWER


For the transformer:
-------------------

Aim for internal impedance as low as 10 mOhm
by low number of turns for output of less than
3V with a continuous power rating of 400W or
more? (to be investigated)

Reasons:

For the same total power, a larger portion is
used where it belongs in the metal piece or
bond, and not for heating the transformer.

In more marginal transformer designs, a resulting
higher CONTINUOS output current can be reached -
preferable, as the heat generated is proportional
to the current squared.

Less arcing as welding is not intended.



For adjusting the average current:
---------------------------------

An adjustable AC switching regulator of the TRIAC type
is only suitable if it secures the the same minimum
properties like the one described in STs AN308 paper, p9

Reasons:

A minimum of power loss

No extra separate secondary winding turns needed,
better used for increasing wire area of a single
winding to minimise impedance.

Fine grained power control - no steps

Can limit the loading of the transformer to it's
intended continuous rating

Blocks the damaging current surge of +400A
decaying for 0.2 sec. to appear, even with no
'soft start' included, if the power control is
set to less than 75 percent.


Minimum property to look for or ask about
if searching for an equivalent ready made
TRIAC controller:

Can handle a kilo watt transformer without
causing asymmetric driving of positive/negative
half periods or the 'rectification' syndrome when
adjusted over the full power range.


Preferable function:

External isolated power-on control port


A bit less important:

Soft Start, preferably with 50 percent power
at the first period or first very few.


Let us know if anyone finds such a rare TRIAC controller,
verified with scope while fully loaded and swept over the
full control range and still dirt cheep. [/pre]